For influencing the mixture formation and charge movement in cylinders of piston internal combustion engines with external auto-ignition, it is known from reference WO 91/14858 to provide means in the intake valve region, which permit a controlled deflection of the flow from the intake area, through the intake opening and into the cylinder. This deflection is intended to improve the poor fuel evaporation resulting from insufficient mixture formation due to a lack of negative pressure in the suction pipe. Sliding valves, butterfly valves, swivel nozzles or the like, arranged in the area directly adjacent to the intake opening, are suggested as means for deflecting the flow. These elements are actuated with respective adjusting means and via a control device, in dependence on the operating state of the motor. For specific operating states, the flow of the fuel-air-mixture flowing through the channel-type intake, henceforth also called gas flow, is deflected through a deflection and speed increase, such that a defined flow, for example a so-called tumble flow, forms inside the cylinder chamber during the intake stroke. The rotational axis of this flow essentially extends crosswise to the cylinder axis. The disadvantage of this arrangement is that the actuation means are positioned in the intake area, directly in front of the intake opening, meaning in a region having already limited space for additional components.
The reference DE-A-197 33 139 discloses the use of an electromagnetic actuator for opening and/or closing a gas intake valve in two opening stages. For this, the actuator is provided with an additional magnet that makes it possible to open the valve even with a minimum stroke. However, no measures for influencing the flow conditions are provided besides the influencing of the opening times since this actuator can only actuate the xe2x80x9copenxe2x80x9d and xe2x80x9cclosedxe2x80x9d position of the gas intake valve and only for two opening widths.
Thus, it is the object of the invention to create a method, which influences the mixture formation and the charge movement by actuating the valve drives via a control device for different load conditions, in particular at low speeds and/or for a small load.
This object is solved according to the invention with a method of influencing the mixture formation and charge movement in the cylinders of a piston internal combustion engine, having at least one gas intake valve and at least one gas outlet valve per cylinder, which are each provided with a fully variable, preferably electromagnetic valve drive and can be actuated via an electronic control device that is configured such that at predetermined speed ranges and/or for predetermined load conditions, at least some of the gas intake valves and/or the gas outlet valves can be moved, respectively in dependence on the piston stroke, with a changeable stroke course, relative to the opening and closing moments and/or the opening time, the opening width and/or the opening duration and/or the movement speed. By purposely influencing the stroke course in this way, it is possible to optimally adapt the mixture preparation and the charge movement to the requirements of the respective load case. For example, the combustion chamber can be filled with a more highly processed fresh mixture by initially opening up only to a small valve cross section and subsequently opening up to a larger valve cross section, which may still be smaller than the full cross section. During the first phase of the stroke movement, the fuel-air-mixture flows with a high flow speed through the only slightly opened cross-sectional area of the valve and into the combustion chamber. The preparation and homogenization of the mixture is thus positively reinforced. A constant, small cross-sectional valve opening is actuated only for the no-load condition. The same is true for piston internal combustion engines with direct fuel injection into the cylinder, for which a flow guidance of the air filling is provided instead of the suctioned-in fresh mixture. The required charge amount for displaying a desired partial load point is ensured in that following a slight or even slow opening of the valve at the start of the opening phase, the valve is subsequently controlled to open up further. Thus, the combustion chamber is filled to an optimum level with fresh mixture for the given load point. Since the stroke course for the gas intake valve can be actuated fully variable via the electromagnetic valve drive and with the electronic control device, the stroke course for the reversing valves (gas intake valve and/or gas outlet valve) can be xe2x80x9cformedxe2x80x9d in dependence on the piston stroke with respect to the opening width and/or the opening duration and/or the movement speed. By varying these parameters, it is possible to optimize the flow conditions upon entering the combustion chamber and inside the combustion chamber.
The method can be modified in different ways. For example, it is possible to open the gas intake valve only briefly and slightly and with increasing movement speed at the start of the valve-opening time. Subsequently, the valve is closed again with high movement speed and, following this, opened once more to a larger cross section. As a result, a movement is excited in the cylinder chamber with a first, low mixture filling and increasing vacuum pressure. Thus, if a larger valve cross-sectional area is subsequently opened up due to the increased vacuum pressure in the cylinder and the dynamic pressure in the gas intake channel in front of the gas intake valve, the charge amount can flow with high speed into the cylinder.
On the other hand, following an initial opening of a larger valve cross section, it is also possible to reduce the gas intake valve at first back to a smaller cross-sectional area and then close it completely. This mode of operation again allows a residual amount of fresh gas to flow at high speed into the cylinder near the end of the opening time, thereby favorably influencing the charge movement in the cylinder during the intake stroke, preferably toward the end of the intake stroke. The stroke course in this case can also be xe2x80x9cformedxe2x80x9d through an optimum adaptation to different load points, by means of a corresponding programming of the control device. Different performance characteristics can be specified for all load cases under consideration.
The above-described different modes of operation can be optionally combined, depending on the load requirements. For internal combustion engines provided with several gas-intake valves for each cylinder, all gas-intake valves or only one gas intake valve of the respective cylinder can also be actuated in this way.